Response of grapevine canopies to chemical elicitors that induce disease resistance

This report presents preliminary outcomes of the PhD project of Ms Angela Smith,
supervised by Drs Kathy Evans and Steve Wilson at the Tasmanian Institute of Agricultural Research, University of Tasmania. Bayesian modelling was used to describe the area of colonisation by Erysiphe necator, the cause of powdery mildew, on all leaves of shoots of Vitis vinifera cv. Cabernet Sauvignon with two different rates of leaf emergence. Shoots with a higher rate of leaf emergence prior to inoculation with E. necator developed powdery mildew more severely. At both rates of leaf emergence, there was a strong association between leaf position for maximum severity of powdery mildew and the position of the leaf in the sink to source transition for carbohydrate, immediately after it had ceased importing photosynthates. Thermal time (degree days) was used to predict the rate of leaf emergence and leaf area development for Chardonnay and Pinot Noir vines grown commercially in southern Tasmania with shoots positioned vertically or by the Scott Henry method. This
report describes how these empirical models, derived from the glasshouse and field data, can be applied for timing disease management strategically and for quantifying dynamic changes in the grapevine canopy structure for susceptibility to powdery mildew and hence disease risk. As susceptibility of leaves to powdery mildew represents the inoculum load for grape berry infection, small changes in management practices may have profound effects on disease expression on the berries. The report concludes with communication outcomes and recommendations for future research and development.